The present invention relates to a linear compressor (vibration type compressor) for use in a refrigerator-freezer, an air conditioner or the like.
A refrigerant CFC-12 (dichlorodifluoromethane, CCI2F2) or HCFC-22 monochlorodifluoromethane, CHCIF2) has been primarily utilized in conventional compressors for use in a refrigerating cycle or the like. However, in view of the influence of ozone layer damage on the human body or other living things or on the global warming, an HFC-based refrigerant containing no chlorine (CI) atoms in a molecule, such as HFC-134a (1,1,1,2-tetrafluoroethane, CH2FCF3), has come to be used.
In recent years, as disclosed in Japanese Laid-open Patent Publication No. 8-200224, an inflammable refrigerant such as propane or isobutane or a natural refrigerant is gradually utilized in reciprocating compressors, rotary compressors, scroll compressors or helical blade compressors.
As compressors other than those referred to above, Japanese Laid-open Utility Model Publication No. 58-116784 discloses a linear compressor.
A conventional linear compressor is explained hereinafter with reference to the drawings.
FIG. 6 depicts a conventional linear compressor having a compression mechanism 1 that includes a motor 3, a cylinder 5, a bearing 6, a piston 8, a cylinder head 10 and a resonant spring 11, and is elastically supported by suspension springs (not shown) within a closed casing 2. The motor 3 includes a stationary element 4 and a movable element 7 secured to the piston 8.
The cylinder 5 and the bearing 6 axially movably support the piston 8. The resonant spring 11 has one end secured to the movable element 7 of the motor 3 and the other end secured to the bearing 6, and a portion thereof is submerged under lubricating oil 12 stored within the closed casing 2. 8a denotes a compression chamber defined by the cylinder 5 and the piston 8. A refrigerant gas introduced into the compression chamber 8a through a suction hole 8b in the piston 8 is compressed via a reciprocating motion of the piston 8.
The lubricating oil 12 stored at a lower portion within the closed casing 2 is stirred by expansion and contraction of the resonant spring 11 following the axial reciprocating motion of the piston 8. The lubricating oil 12 then scatters within the closed casing 2 to lubricate the sliding portions between the piston 8 and the cylinder 5, and the sliding portions between the piston 8 and the bearing 6.
The refrigerant used is CFC-12 or HCFC-22 that has been hitherto used primarily in a cooling system, while mineral oil is primarily used for the lubricating oil 12.
Cast iron or an aluminum-based alloy is used for the sliding members constituting the sliding portions such as the cylinder 5, piston 8, bearing 6 and the like. In some cases, surface treatment such as manganese phosphate-based chemical conversion coating is applied thereto.
However, the lubricating oil 12 is used in the conventional linear compressors, and some lubricating oil is used in the compressors such as the reciprocating compressors, rotary compressors, scroll compressors or helical blade compressors, in which a natural refrigerant or an inflammable refrigerant is used. The use of the lubricating oil 12 lowers the heat exchanging efficiency in the cooling system, thus giving rise to the possibility of lowering the efficiency of the cooling system.
By way of example, considering the case where the aforementioned refrigerant is used in the compressors, for example, the conventional linear compressors, in which an inflammable refrigerant or natural refrigerant such as propane, isobutane, carbon dioxide or the like is used, the inflammable refrigerant or natural refrigerant dissolves in the lubricating oil 12 within the compressors. In particular, hydrocarbons dissolve in the lubricating oil 12 in larger amount than other refrigerants. Because of this, the amount of refrigerant required for the cooling system must be increased by the amount that dissolves in the lubricating oil, compared with the cooling system in which no lubricating oil is used. In particular, when hydrocarbons are used, it has been considered that the amount of refrigerant must be further increased.
The use of an increased amount of the natural refrigerant or inflammable refrigerant results in an increase in cost, and if the refrigerant leaks, there is a possibility of catching fire or explosion.
Furthermore, because the compression mechanism 1 is arranged horizontally in the conventional linear compressors, a lateral load is applied to the sliding portions between the piston 8 and the cylinder 5 and between the piston 8 and the bearing 6 by the weight of the piston 8, the movable element 7 of the motor 3 and the like. This increases the sliding loss, and if no lubricating oil is used, there is a good chance that the sliding portions may be subjected to wear or seizing.
The present invention has been developed to overcome the above-described disadvantages.
It is accordingly an objective of the present invention to provide an inexpensive, safe and highly reliable linear compressor capable of reducing the amount of refrigerant for use in the cooling system, improving the heat exchanging efficiency in the cooling system, and also improving the efficiency of the whole cooling system.
In accomplishing the above objective, the linear compressor according to the present invention is characterized by including a closed casing and a compression mechanism arranged vertically within the closed casing for compressing and discharging a refrigerant, wherein an inflammable refrigerant or a natural refrigerant is used as the refrigerant while no lubricating oil is filled up.
According to the above-described construction, because no lubricating oil is used, the heat exchanging efficiency in a cooling system is improved and the efficiency of the whole cooling system is improved. Furthermore, because the refrigerant does not dissolve in the lubricating oil, the amount of refrigerant to be used in the cooling system is reduced, and the cost is also reduced. Even if the refrigerant leaks, the possibility of catching fire or exploding is reduced, enhancing the safety.
The use of propane, isobutane or carbon dioxide for the refrigerant does not cause any problem associated with ozone layer damage, thus enhancing the safety.
If a sliding surface in the compression mechanism is surface-treated with Teflon TM (polytetrafluoroethylene), molybdenum disulfide and alumite, the self-lubricating effect of a surface-treating agent prevents abnormal wear at the sliding portion of a piston and a cylinder even without any lubricating oil, thus enhancing the reliability. Also, the surface treatment reduces the coefficient of friction on the sliding portion and reduces the sliding loss, thus enhancing the compressor efficiency.
In another aspect of the present invention, a linear compressor is characterized by including a closed casing, a compression mechanism arranged horizontally within the closed casing for compressing and discharging a refrigerant, and means for reducing a lateral load applied to a sliding surface in the compression mechanism, wherein an inflammable refrigerant or a natural refrigerant is used as the refrigerant while no lubricating oil is filled up.
According to the above-described construction, because no lubricating oil is used, the heat exchanging efficiency in a cooling system is improved and the efficiency of the whole cooling system is improved. Furthermore, because the refrigerant does not dissolve in the lubricating oil, the amount of refrigerant to be used in the cooling system is reduced, and the cost is also reduced. Even if the refrigerant leaks, the possibility of catching fire or exploding is reduced, enhancing the safety.